Search

The potential to increase biofuel output from a fast pyrolysis-based biorefinery through hydrogen enhancement is assessed for thermal fast pyrolysis (TFP) and catalytic pyrolysis (CAT) processes featuring bio-oil upgrade into gasoline, diesel and heavy hydrocarbon fractions. Results show that utilizing pyrolysis process off-gases to produce synthetic natural gas with an external hydrogen source could provide up to 48.2% (TFP) and 61.2% (CAT) reductions in biomass resource utilization. These savings are enabled by significantly improved carbon efficiency of the hydrogen enhanced designs, with efficiencies increasing from 40.5% to 66.3% for TFP and from 28.9% to 58.6% for CAT. Although the CAT process has a lower biofuel yield than the TFP process, it has a higher potential for hydrogen enhancement and achieves a higher biofuel output than TFP when fully enhanced with external hydrogen. The trade-off to the improved biofuel yield (higher carbon efficiency) is the substantial need for electricity to produce hydrogen via electrolysis, as for every megajoule (MJ) of biomass feedstock, 0.65–0.66 MJ of electricity is needed for the electrolyser.

A model for pressurised steam/O2-blown fluidised-bed gasification of biomass with catalytic reforming of hydrocarbons and tars was developed using Aspen Plus simulation software. Seven main blocks were used to model the fluidised-bed gasifier and two for the catalytic reformer. Modelling blocks were complemented with FORTRAN subroutines to simulate the observed non-equilibrium behaviour of the process. The model was fitted with experimental data derived from a 0.5 MW scale test rig operated with crushed wood pellets and forest residues and was shown to be capable of predicting product gas composition from gasification of clean wood. A parametric analysis indicated that a significant improvement in the syngas efficiency could be achieved by rising the filtration temperature and reformer conversions. Other improvement possibilities include fuel drying and lower reforming temperature.